Locomotion can be described as movement from one place to another. Crawling and creeping mechanics are essential in the overall development of early locomotion. Crawling can be defined as moving slowly by dragging the trunk (i.e., abdomen) and lower extremities along the ground. The defining component of crawling is that the child's belly is in contact with the floor. This is distinguished from creeping, which means to move across the floor on hands and knees without the trunk being in direct contact with the surface.
The transition from a prone to the quadruped posture typically occurs around six to seven months of age. FIGS. 1-4 show perspective views of an infant during this transition. In a first intermediate posture in FIG. 1, the infant's arms are extended before him and his arms, trunk and lower extremities are largely resting on the ground. The infant's forearms remain fully in contact with the floor surface, while he is bearing weight through his shoulders to his elbows. In a second intermediate posture in FIG. 2, the infant begins to extend his elbows and transfer upper extremity weight from forearms to hands so that his forearms begin to lift off the ground. Subsequently, in a third intermediate posture in FIG. 3, the infant begins to push his body posteriorly (i.e., in a backwards direction), raising the buttocks into the air while shifting his weight from his hips towards the knees. At the same time, the infant continues extending his arms at the elbows and transferring upper extremity weight from forearms to hands. Finally, in the quadruped posture shown in FIG. 4, the infant is bearing his weight on this hands and knees while maintaining hands under shoulders and knees under hips.
The quadruped posture requires the ability to maintain a steady position in a weight bearing, antigravity posture, and thus requires significant strength and stability at the hip and shoulder joints to maintain correct alignment and position. As a result, in early stages of learning to achieve this posture, an infant will often assume an “immature quadruped” posture during the transition. Such an immature quadruped posture is shown in the perspective view in FIG. 5. In this posture, the infant's hips are in external rotation and abduction (arrow), and his lower extremities are in poor weight bearing alignment (i.e., knees not under hips). The immature quadruped posture may be due to underdeveloped abdominal musculature as well as strong contraction of hip flexors in order to stabilize the posture. The splayed positioning of the immature quadruped posture aids stability, but interferes with locomotion.
Once stability is ultimately gained in the quadruped posture, the infant can begin to work on controlled mobility in efforts to creep with his hands and knees. Controlled mobility can be defined by the ability to alter a position or move in a weight bearing position while maintaining postural stability. Static-dynamic control is a prerequisite for the final skill stage of motor control. The process of weight shifting in various directions occurs in efforts to encourage forward and backward movement while on hands and knees. With controlled weight shifts, the child will typically rock forward and backward in efforts to lift one limb at a time, eventually lifting one upper extremity and the opposite lower extremity at once. This movement leads to creeping in the quadruped posture at approximately eight to ten months in typical development. Both the upper and lower extremities participate equally in creeping as the child advances in the direction of movement.
Unfortunately, both the transition from fully prone to quadruped, as well as early locomotion may be frustrated by environmental factors such as insufficient frictional coupling between the infant and the ground. Accordingly, there is a need for innovations that aid an infant in achieving a stable quadruped posture as well as developing controlled mobility with crawling and creeping mechanics, particularly on surfaces with low friction.